One of the best tools that you have as gardeners to help us estimate your gardening schedule is the USDA zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

You should be able to estimate when it's a good idea to plant asparagus fern by referring to the USDA zone info for Boulder.

Planting Calendar for Asparagus Fern

Frost tolerance for asparagus fern:	Not tolerant of frost.
When to plant:	After the last frost has passed.

Asparagus Fern do not do well in cold weather which means that you must wait until it warms up after the last frost before you can plant them.

The earliest that you can plant asparagus fern in Boulder is April. However, you really should wait until May if you don't want to take any chances.

The last month that you can plant asparagus fern and expect a good harvest is probably August. You probably don't want to wait any later than that or else your asparagus fern may not have a chance to grow to maturity. Starting your asparagus fern indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

In Boulder the average date of last frost happens on April 15. You can expect an average low temperature of -15°F in the coldest months of winter.

Since the USDA zone info for Boulder is not always accurate the actual date of last frost will vary from year to year. Since half of the time in Boulder it frosts late in the year after April 15 be ready to cover your asparagus fern if you have a late frost.

USDA Zone Info for Boulder

Here is the info for USDA Zone 5b.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-15°F
Highest Expected Low	-10°F

This means that on a really cold year, the coldest it will get is -15°F. On most years you should be prepared to experience lows near -10°F.

Plants to Grow in Boulder

You may be interested in your other planting guides for Boulder.